1800: Smiths Instruments

[Kev415]

Hi
Does anyone know the thread size of the knurled thumb nut for the retaining brackets on the back of the smiths instruments? It doesn't match any of my thread gauges. (Through elimination I can confirm its not 3BA, 4BA, metric or 10-32!)

[Ron Kwas]

Kev;

I just checked a junk P1800 Tach (with two fairly beat up and rusty studs)...it was close to 8-32...also close to 4mm X.5 thread, but neither felt right...so I measured the thread-count per inch and found it to be 34(!!)...maybe that's their way of assuring the securing thumbscrew (in 8-32) locks in place and doesn't vibrate off!...maybe it's a "special thread" (I've run across these in the industrial instrumentation world also)...
...so I also called Nisonger (Instrument rebuilding specialist in New York, they are on-line, if you want to send them an e-mail directly) and they noted that these are British (no surprise there...), and maybe special thread (I agree there!)...and that they are made for them in Britain, but he didn't know threadsize of-hand...that's all info I was able to ascertain...

Good Hunting!

[harpgirl]

Hi,
I don't know the answer to this question but found this thread (no pun intended) which has quite a few suggestions including 2BA and the suggestion of a switch to UNF later in production.

http://www.britishcarforum.com/bcf/a...p/t-58337.html

I hope that is some help.

[Derek UK]

Try https://speedycables.com/ or http://www.speedograph-richfield.com/index.html
My guess would be 3BA.

[tjrvp]

I had the same issue. The clocks are different to the tach and speedo. after much trial and error I used 3BA nylon Large on the tach and an m3 nylon thumbs screws on the clocks the nylon being soft enough not to damage thread